1. Field of the Invention
The present invention relates to a novel and inventive axle driving apparatus for running vehicles, comprising a combination of two hydraulic transmissions (hereinafter referred to as HST), one for forward-rearward drive switching and changing speed, and the other for steering, wherein a steering device such as a steering wheel is manipulated in the same direction to turn the vehicle in the right or left direction regardless of whether the vehicle is running forward or rearward.
2. Related Art
A running vehicle having a configuration in which a pair of right and left driving axles are driven separately by a pair of HSTs is well known. One example thereof is disclosed in U.S. Pat. No. 4,782,650. In such a vehicle, the output rotational speeds of the two HSTs are rendered to coincide with each other when the vehicle is running straight, and are differentiated when the vehicle turns right or left.
In the conventional vehicle having two HSTs as described above, the HSTs, together with the link mechanism and the axles associated with the HSTs, require high precision in fabrication and assembly to accomplish an exact coincidence of the output rotational speed of the HSTs when the vehicle is driving straight. Also, considerable time is required for output adjustment of the left and right driving axles before shipment. Assuming that the pump or motor capacity is different between the two HSTs due to a fabrication error or the like, it is possible to make adjustments to assure the same rotational speed of the right and left axles when the vehicle is running straight. When the vehicle turns right or left, however, the steering feel is different between right and left turns, thereby making the vehicle difficult to maneuver.
With such a vehicle, a pair of HSTs are normally juxtaposed on right and left sides, which in turn increases the vehicle width, resulting in difficulty for the vehicle to make a small turn. Also, in the case of a specialty vehicle, the job efficiency is adversely affected.
One solution to the problem of an axle driving apparatus having two combined HSTs is a configuration in which one HST is used for speed change with a pair of axles power-coupled to a normal differential arrangement for differential coupling and the other HST is used for steering with an output rotation thereof applied through another steering differential arrangement to the two axles for rotation in opposite directions, so that at the time of steering, one axle is increased in speed by the output from the steering differential arrangement, and the other axle is decreased in speed. This turns the vehicle toward the side of the decelerating axle.
In this configuration, the rotational direction of the steering HST is switched according to the direction in which the steering wheel or other steering means is manipulated. Even when the steering wheel is manipulated in the same direction, the axle operatively coupled to the speed-change HST is rotated in the opposite direction depending on whether the vehicle is running forward or rearward. Thus, the axle increased in speed when the vehicle is running forward is decreased in speed when the vehicle is running rearward, and vice versa. In a configuration in which the steering means is a steering wheel, counterclockwise rotation of the steering wheel in the forward drive mode decelerates the left axle and accelerates the right axle to turn the vehicle to the left. If, however, the steering wheel is rotated counterclockwise when the vehicle is running in reverse, the left axle is accelerated while the right axle is decelerated, thereby causing the vehicle to turn to the right. In other words, for the vehicle to turn left while running in reverse, the steering wheel is required to be rotated clockwise. This gives the driver a driving feel that is considerably different from one normally experienced in passenger cars. This may lead to an increase in traffic accidents due to a driving error.
According to the present invention, there is provided an axle driving apparatus comprising a pair of axles, a speed-change HST including a fluid pressure pump of variable capacity type and a motor of fluid pressure type coupled to each other through a fluid, a first differential arrangement powercoupled to the output means of the motor of the speed-change HST for differentially coupling the axle pair to each other, a steering HST including a fluid pressure pump of variable capacity type and a motor of fluid pressure type coupled to each other through a fluid, a second differential arrangement powercoupled to the output means of the motor of the steering HST, a pair of steering output shafts differentially coupled to each other through the second differential arrangement, a first transmission train interposed between one of the steering output shafts and one of the axles, and a second transmission train interposed between the other steering output shaft and the other axle for transmitting the turning effort to the other axle in the direction opposite to that of the first transmission train, by which the steering operation means is operated in the same direction to turn the vehicle in the same direction regardless of whether the vehicle is running forward or rearward.
In a first configuration to achieve this object, a vehicle comprises a forward/rearward setting operation means, speed-change operation means and steering operation means. In the axle driving apparatus, on the other hand, first adjusting means is provided which, by changing the position thereof, can change the capacity and the rotational direction of the pump of the speed-change HST. Also, a first rotary member is rotated with a first rotary shaft for changing the position of the first adjusting means. A first link mechanism is interposed between the speed-change operation means and the first rotary member. The first link mechanism includes a first link connected to the first rotary member at a changeable position while at the same time being coupled to a forward/rearward drive setting operation means. A second adjusting means is provided also which, by changing the position thereof, is capable of changing the capacity and the rotational direction of the pump of the steering HST. A second rotary member is rotated with a second rotary shaft for changing the position of the second adjusting means. A second link mechanism is interposed between the second rotary member and the steering operation means. The second link mechanism includes a second link connected to the second rotary member at a changeable position while at the same time being coupled to the forward/rearward drive setting operation means. In accordance with the switching of the forward/rearward drive setting by the forward/rearward drive setting operation means, the position of the first link connecting the first rotary member and the position of the second link connecting the second rotary member are changed.
In this first configuration, when the forward/rearward drive setting is switched by the forward/rearward drive setting operation means, the position of the first link connecting the first rotary member is changed, so that the output rotation of the speed-change HST is reversed and the axle rotates in the opposite direction. At the same time, however, the position of the second link connecting the second rotary member is also changed.
When the steering operation means is operated in the same direction, the output rotation of the steering HST is reversed between when the vehicle is running forward and when it is running rearward. Thus the axle acceleration and deceleration remain unchanged regardless of whether the vehicle is running forward or rearward. For this reason, the vehicle body can be turned in the same direction by operating the steering operation means in the same direction whether the vehicle is running forward or rearward.
In this configuration, the first rotary member may include a first guide means so that the first link is connected to the first rotary member through the first guide means at a changeable position, and the second rotary member may include a second guide means so that the second link is connected to the second rotary member through the second guide means at a changeable position. This makes it possible to change the connecting position of the first and second links smoothly with respect to the first and second rotary members, respectively.
Further, at least one of the first guide means and the second guide means may be a hole slidably fitted in a part of the first link or the second link, as the case may be. The machining cost can thus be saved with a simple configuration.
Next, in a second configuration to achieve this object, a forward rotation/reverse rotation switching transmission mechanism is interposed between the output means of the motor of the steering HST and the input means of the second differential arrangement. When the steering operation means is operated in the same direction, the motor of the steering HST is rotated in the same direction whether the vehicle is running forward or rearward. The direction of rotation of the steering output shaft is reversed, however, by switching the forward rotation transmission and the reverse rotation transmission by the forward rotation/reverse rotation switching transmission mechanism so that the motor output is transmitted to the second differential arrangement.
In one configuration of the forward rotation/reverse rotation switching transmission mechanism, a selective coupling means is provided by which the forward rotation transmission train is coupled to the input means of the second differential arrangement, the reverse rotation transmission train is coupled to the input means of the second differential arrangement or one of the forward rotation transmission trains and the reverse rotation transmission train is selectively coupled to the output means of the motor of the steering HST.
In this configuration, the forward/rearward drive setting switching means is provided outside of the housing, and the selective coupling means selects the forward rotation transmission train or the reverse rotation transmission train in accordance with the switching of the forward/rearward drive setting by the forward/rearward drive setting operation means, thereby coupling the selected train to the output means of the motor of the steering HST.
In this regard, the output means of the motor of the steering HST may be an output shaft, and the selective coupling means may be a sliding gear arranged slidably on the output shaft and not relatively rotatably. Further, assuming that the forward rotation transmission train and the reverse rotation transmission train may both include a gear adapted to engage the sliding gear, the sliding gear may selectively engage one of the forward rotation transmission input gear and the reverse rotation transmission input gear.
As an alternative, the selective coupling means may include a sliding gear arranged slidably on the output shaft of the HST motor for steering and not relatively rotatably and a clutch attached to the sliding gear. A gear adapted to engage the sliding gear may be arranged on one of the forward rotation transmission train or the reverse rotation transmission train. A clutch adapted to engage the first clutch described above may be included in the forward rotation transmission train or the reverse rotation transmission train. The engagement of the sliding gear or the engagement of the first clutch can be selected.
In another configuration of the forward rotation/reverse rotation switching transmission mechanism, the forward rotation/reverse rotation switching transmission mechanism includes a forward rotation transmission train coupled to the input means of the second differential arrangement, a first electromagnetic clutch for permitting the forward rotation transmission train to engage or disengage from the output means of the motor of the steering HST, a reverse rotation transmission train coupled to the input means of the second differential arrangement and a second electromagnetic clutch for permitting the reverse rotation transmission train to engage or disengage from the output means of the motor of the steering HST. The forward/rearward drive setting operation means is arranged outside of the housing, so that the first electromagnetic clutch or the second electromagnetic clutch is selectively engaged by the forward/rearward setting operation means switching the forward/rearward drive setting.
The other object, features and advantages of the present invention are more fully understood from the following description.